This invention relates generally to glass-ceramic cooktop appliances and more particularly to methods and devices for sensing properties relating to the appliance, such as temperature of the glass-ceramic cooktop surface, properties of cooking utensils placed on the cooktop, and properties of the utensil contents.
The use of glass-ceramic plates as cooktops in cooking appliances is well known. Such glass-ceramic cooktops have a smooth surface that presents a pleasing appearance and is easily cleaned in that the smooth, continuous surface prevents spillovers from falling onto the energy source underneath the cooktop.
In one known type of glass-ceramic cooktop appliance, the glass-ceramic plate is heated by radiation from an energy source, such as an electric coil or a gas burner, disposed beneath the plate. The glass-ceramic plate is sufficiently heated by the energy source to heat utensils upon it primarily by conduction from the heated glass-ceramic plate to the utensil. Another type of glass-ceramic cooktop appliance uses an energy source that radiates substantially in the infrared region in combination with a glass-ceramic plate that is substantially transparent to such radiation. In these appliances, a utensil placed on the cooktop is heated partially by radiation transmitted directly from the energy source to the utensil, rather than by conduction from the glass-ceramic plate. Such radiant glass-ceramic cooktops are more thermally efficient than other glass-ceramic cooktops and have the further advantage of responding more quickly to changes in the power level applied to the energy source. Yet another type of glass-ceramic cooktop appliance inductively heats utensils placed on the cooktop. In this case, the energy source is an RF generator that emits RF energy when activated. The utensil, which contains an appropriate material, absorbs the RF energy and is thus heated.
In each type of glass-ceramic cooktop appliances, provision must be made to avoid overheating the cooktop. For most glass-ceramic materials, the operating temperature should not exceed 600-700.degree. C. for any prolonged period. Under normal operating conditions, the temperature of the glass-ceramic plate will generally remain below this limit. However, conditions can occur which can cause this temperature limit to be exceeded. Commonly occurring examples include operating the appliance with no load, i.e., no utensil, on the cooktop surface, using badly warped utensils that make uneven contact with the cooktop surface, and operating the appliance with a shiny and/or empty utensil.
To protect the glass-ceramic from extreme temperatures, glass-ceramic cooktop appliances ordinarily have some sort of temperature sensing device that removes power from the energy source if high temperatures are detected. In addition to providing thermal protection, such temperature sensors can be used to provide temperature-based control of the cooking surface and to provide a hot surface indication, such as a warning light, after a burner has been turned off.
One common approach to sensing temperature in glass-ceramic cooktop appliances is to place a temperature sensor directly on the underside of the glass-ceramic plate. With this approach, however, the temperature sensor is subject to the high burner temperatures and thus more susceptible to failure. Moreover, the sensor detects some average flux and does not produce a direct measurement of the glass-ceramic temperature. Thus, it is desirable to use an optical sensor assembly that "looks" at the glass-ceramic surface from a remote location to detect the temperature of the surface. Remote sensor assemblies are also capable of "looking" through the glass-ceramic plate to detect characteristics of a utensil placed on the cooktop, such as the temperature, size or type of the utensil, the presence or absence of the utensil, or the properties, such as boiling state, of the utensil contents.
Variations in the field of view of remote sensor assemblies can affect their performance in detecting the properties of a cooktop and/or utensil. Such variations can occur due to differences between individual burner assemblies, manufacturing variations, and the reuse of common parts across various burner models and products. If the field of view of individual sensor assemblies is not properly adjusted, then the accuracy of the sensor's measurements will suffer.
Accordingly, there is a need for a remote sensor assembly that can be calibrated to adjust the field of view and a method for calibrating such an assembly.